Duotones, Tritones, Quadtones, Color Halftones, and Fake Duotones

Learning about duotones can also teach you about the limits of both photography and offset printing in representing the wide range of tones visible in the physical world. On a sunny day you can see a huge number of distinct values ranging from the lightest lights to the darkest shadows. This is true in relation to both the lightness/darkness and the actual hues (the named colors, like red and blue).

Then, when you take a photograph of what you see in the physical world, you cut this range of distinct tones dramatically. Furthermore, when you introduce this photo as a digital image into your page composition software (such as InDesign) and from there into your printer’s digital prepress workflow and on to the pressroom floor, the number of distinct colors and tone values narrows even further. Also, the dark areas aren’t as dark as they are in the physical world, and the light areas aren’t as light.

One way to compensate for this tone compression is to add to the number of inks you are using on press and to focus each separate ink on the details of a particular tonal range in the photo (highlights, midtones, or shadows).

For instance, let’s say you print a duotone using black and green ink. You might want to focus the black ink on producing as much detail in the shadows as possible. And you might choose to use the green ink to enhance the number of distinct tone levels in the midtones or the highlights. However you choose to do this, your goal will be to extend the range of two tonal areas of the photo and hence to increase the nuances of the image detail.

You could even do this with four colors. Some people focus on four distinct regions of the overall tone curve (from highlights to shadows) using cyan, magenta, yellow, and black in percentages that mimic a black-and-white photo (i.e., to omit visible color detail and produce a range of tones approximating black, grey, and white). This is called a quadtone, quadtratone, or 4-color black-and-white image. From a distance, it looks like a black-and-white photo with incredible depth of tone and image detail, but through a printer’s loupe you can see the cyan, magenta, yellow, and black halftone dots.

Other designers might produce a quadtone or a tritone (three inks) with one or two distinct black mixtures and perhaps one or two gray mixtures (think PMS colors rather than process colors). In both cases the goal is to preserve both image detail and the distinction between adjacent tones.

Either way (and whether you’re producing a duotone, tritone, or quadtone in Photoshop), you can also choose to enhance one of the colors and make it dominant. A green and black duotone, for instance, might include an overall greenish cast for an aesthetic effect to make it more striking than a black-predominant duotone.

One thing I have found useful over the years is to use the preset duotone curves available in Photoshop, which allow you to benefit from other designers’ experience. Instead of setting a halftone curve for each of the two colors in a duotone yourself, you can use predetermined tone curves that enhance highlights, midtones, or shadows and then view the results on a computer screen.

Unfortunately, since duotones are often made with a PMS color and black, you cannot (absolutely) accurately proof a duotone on an inkjet proofing device or any other printer based on cyan, magenta, yellow, and black ink. Rather, you would have to pay for a press proof (an actual short press run produced on a small offset press) to see an absolutely accurate rendition of what you can expect for the final product.

An alternative would be to live with an inkjet proof and then attend a press inspection to see the final result before the print job is trimmed, folded, and delivered. In this case you would have a little leeway in increasing one or the other duotone color. Keep in mind that such an adjustment could affect the entire job. If you saw a serious problem, you would need to stop the press, adjust the duotones in prepress (change the tone curves in Photoshop and then replace the images in InDesign), and then burn new printing plates. This would be very expensive. Hence, using preset duotone tone curves is often a wise choice.

Beyond actual duotones, tritones, and quadtones, there are two other options involving color.

One is called a fake duotone. This is created by printing a flat, even screen of a color, like a light green, as a background, and then printing a black-and-white halftone over this light green background screen. You could identify a fake duotone in a printed piece by the absence of any true white (i.e., highlight areas) within the fake duotone. After all, the green would be an undifferentiated, rectangular tint screen of color, not a halftone with highlights and shadows.

The other, similar approach to adding a color to a photo is a colored halftone. Using the green tone noted above as an example, your halftone would include only one color (not two, like a duotone). And you would not see any true black or gray tones in the photo. The darkest dark areas would only be 100 percent of the presumably very dark, green ink (to keep these examples consistent).

You may want to locate examples of these options online (with Google Images) to see the subtle differences. My personal preference would be to create a duotone rather than a fake duotone. Why? Because of the nuances of color and tone, the gradual shift from one color to the other in a duotone, and the exceptional detail. To me, the fake duotone looks less interesting because the background is just a flat screen of color. That said, there may be an artistic effect you’re trying to achieve that a fake duotone will suit perfectly. Use your aesthetic judgment.

In contrast, there are good reasons to choose a colored halftone. First of all, if you’re printing a halftone in color, you’re (presumably) not adding an additional ink color to the printing press (maybe you’re using an accent color that’s already available). Hence the cost may be a determining factor.

That said, from an aesthetic viewpoint, since there would be no black plate to add depth and intensity to the image, a green halftone might provide a more ethereal look than a duotone. Again, knowing the technical approaches can give you more options to consider based on the visual effect you seek.

To be absolutely certain you are communicating your goals, it never hurts to discuss duotones, fake duotones, and color halftones with your printer prior to job submission. If you can provide printed samples of the duotone effect you want to achieve, all the better. Your printer can then adjust the Photoshop tone curves for each of the duotone colors to better achieve the effect in your printed sample.

It also helps to choose a printing supplier with sufficient skill and knowledge in creating duotones (i.e., ask for samples of your printer’s own duotone work). This will be particularly important when you’re printing on an uncoated paper stock. Uncoated paper is more absorbant than coated paper. Therefore, the tone curves for the duotone may need to be reduced. Otherwise, your presumed correct amount of ink may spread into the uncoated paper fibers and unduly darken the image, diminishing the duotone appearance you’re after.

So the smartest thing you can do is discuss duotones with your printer early in the printing process, share samples to make sure you’re communicating effectively, and ask for the printer’s samples and suggestions.

[Steven Waxman is a printing consultant. He teaches corporations how to save money buying printing, brokers printing services, and teaches prepress techniques. Steven has been in the printing industry for thirty-three years working as a writer, editor, print buyer, photographer, graphic designer, art director, and production manager.]